1. Field of the Invention
The present invention relates to a vacuum belt conveyor, and, more particularly, to a vacuum belt conveyor for the conveyance of a web.
2. Description of the Related Art
Reference is made to the following documents: DE 299 10 850; U.S. Pat. No. 3,355,349; Brochure xe2x80x9cDouble-Tail-Elimination of the Fibron Machinery Corporation, New Westminster, BC, Canada; DE 199 62 731; DE 199 00 986; DE 100 09 188, which are incorporated herein and made a part hereof. In German Patent 299 10 850 a vacuum belt conveyor is disclosed which includes an air pervious endless belt traveling across two pulleys and a vacuum box. Negative pressure of a vacuum box propagates through the conveying run of the belt in order to draw a web or xe2x80x9ctailxe2x80x9d, to be guided by the conveyor belt, by suction. One of the pulleys is displaceable in order to tension the belt.
According to U.S. Pat. No. 3,355,349, at the infeed or upstream end of the conveyor, a severing device or tail cutter is arranged which includes a toothed knife extending transversely to the pulley axis. Before the belt conveyor begins to convey the tail of a web, the complete web, including the tail, is running (e.g. from a last drying cylinder) downwardly, passing the infeed end of the belt conveyor and finally entering into a waste bin or waste pulper. A small xe2x80x9ctail doctorxe2x80x9d is provided at the last drying cylinder for peeling the tail from the dryer shell and for transferring the tail onto the belt conveyor. When the latter is beginning to operate the tail cutter severs the tail thus forming a new beginning of the tail which is conveyed to the calender. If no tail cutter is present the belt conveyor repulls a xe2x80x9cdouble tailxe2x80x9d upwardly from the waste bin causing problems during the threading operation. Reference is made to the above mentioned brochure xe2x80x9cDouble-Tail Eliminationxe2x80x9d.
According to DE 199 62 731, an improvement has been proposed including an infeed tray. This results in a more reliable operation of the belt conveyor, even with increased working speed. However, there is existing a need for further improvements in the way mentioned hereinbefore.
It is an object of the present invention to provide an improved conveying apparatus which will operate reliably with various paper grades, even with paper grades of high strength, and in modem paper making or finishing machines operating at extremely high speed (e.g. more than 2000 meters per minute).
It is a further object of the present invention to eliminate a tail doctor at the web-delivering roll or cylinder, and to avoid the use of a tail cutter and an infeed tray.
Another object of the invention is an improved design which allows the upstream end of the conveyor closer to a web-delivering surface (e.g. surface of a roll or cylinder) than was previously practiced.
The aforementioned objects, as well as further objects that are presented later, are attained by the features defined herein.
According to the present invention, a belt conveyor further includes a curved and perforated guiding surface for the air-pervious endless belt. The guiding surface is arranged at the upstream end of the conveyor; having the perforations of the guiding surface outwardly open toward the endless belt and inwardly open toward a source of negative pressure.
In operation, the curved and perforated guiding surface acts as a suction pickup area which is placed very close to the traveling path of the web, e.g. close to a web-delivering surface (fabric, felt, roll or cylinder). Thus, the web or tail, in particular a new beginning of the tail, can be transferred onto the conveyor belt in a much shorter time than hitherto possible.
An advantage of the present invention allows the suction pickup area of the vacuum belt conveyor to come directly into contact with the web traveling path so that the tail, in particular a new beginning of the tail, can be transferred directly onto the conveyor belt.
Another advantage of the present invention allows the tail of the web, preferably a new beginning of the tail, to be peeled off from the surface of a roll or cylinder, by at least one marginal nozzle. Immediately thereafter, the tail is picked up by the conveyor belt in the area of the curved and perforated guiding surface.
Yet another advantage of the present invention is an improved threading process in paper machines is obtained, without the need for a tail doctor at the web delivering roll or cylinder. Furthermore, the vacuum belt conveyor does not need an infeed tray. In many cases, a tail cutter may also be avoided.